FIG. 1 illustrates a block diagram of a transceiver module 2 currently used in optical communications. The transceiver module 2 includes a transmitter portion 3 a receiver portion 4. The transmitter and receiver portions 3 and 4 are controlled by a transceiver controller 6. The transmitter portion 3 comprises components for transmitting data in the form of amplitude modulated optical signals over multiple fibers (not shown). The transmitter portion includes a laser driver 11 and a plurality of laser diodes 12. The laser driver 11 outputs electrical signals to the laser diodes 12 to modulate the laser diodes 12, thereby causing them to output optical signals that have power levels corresponding to logic 1s and logic 0s. An optics system (not shown) of the transceiver module 2 focuses the coherent light beams produced by the laser diodes 12 into the ends of respective transmit optical fibers (not shown) held within a connector (not shown) that mates with the transceiver module.
A plurality of monitor photodiodes 14 monitor the output power levels of the respective laser diodes 12 and produce respective electrical analog feedback signals that are delivered to an analog-to-digital converter (ADC) 15, which converts that electrical analog signals into digital signals. The digital signals are input to the transceiver controller 6, which processes them to obtain respective average output power levels for the respective laser diodes 12. The controller 6 outputs controls signals to the laser driver 11 to cause it to adjust the respective bias current signals output to the respective laser diodes 12 such that the average output power levels of the laser diodes are maintained at relatively constant levels.
The receiver portion 4 includes a plurality of receive photodiodes 21 that receive incoming optical signals output from the ends of respective receive optical fibers (not shown) held in the connector referred to above that mates with the transceiver module. An optics system (not shown) of the receiver portion 4 focuses the light output from the ends of the receive optical fibers onto the respective receive photodiodes 21. The connector may include an optics system that focuses light from the ends of the receive fibers onto the optics system of the receive portion of the transceiver module, which then focuses the light onto the photodiodes. The receive photodiodes 21 convert the incoming optical signals into electrical analog signals. An ADC 22 converts the electrical analog signals into electrical digital signals suitable for processing by the transceiver controller 6. The transceiver controller 6 processes the digital signals to recover the data represented by the signals.
The laser driver 11 is typically implemented as an integrated circuit (IC). Likewise, the transceiver controller 6 is typically implemented as an IC. The laser diodes 12, the monitor photodiodes 14 and the receive photodiodes 21 are typically implemented in respective separate ICs. The transceiver module 2 typically includes a printed circuit board (PCB) (not shown) or flex circuit (not shown) to which these ICs are die attached and wire bonded to allow the ICs to communicate with one another as needed. The transceiver module 2 typically also includes a heat spreader device (not shown) for dissipating heat generated by the ICs. The IC in which the laser diodes 12 are implemented has a reliability that is strongly influenced by temperature. The laser diodes may be, for example, vertical cavity surface-emitting laser diodes (VCSELs), which, like other laser diodes, have a performance level that degrades as temperature increases. The laser diode IC generates heat that can detrimentally affect its own performance. In addition, the IC in which the laser diode driver is implemented generates even more heat.
While a heat spreader device is generally effective at dissipating heat generated by the ICs by spreading it out and moving it away from the ICs, the heat spreader device is not always sufficient to prevent the temperature of the laser diode IC from increasing to the point at which laser performance degrades. For example, in one known transceiver module of the type described above with reference to FIG. 1, the VCSEL IC (contains the VCSELs) and the VCSEL driver IC (drives the VCSELs) are attached to a top surface of a flex circuit that is mounted to a top surface of a copper heat spreader device. In this case, heat generated by the VCSEL driver IC flows into the heat spreader device, generating heat in the heat spreader device that flows into the VCSEL IC. Therefore, heat generated by the VCSEL driver IC can increase the temperature of the VCSEL IC, and thus detrimentally affect its performance.
One way to prevent heat generated by the VCSEL driver IC from affecting the VCSEL IC is to position the VCSEL IC and the VCSEL driver IC a substantial distance away from each other on the PCB or flex circuit. By doing this, heat that flows into the heat spreader device from the VCSEL driver IC should not affect the temperature of the VCSEL IC. However, increasing the distance between the VCSEL driver IC and the VCSEL IC can create other problems. In particular, the increased distance results in the electrical paths between the VCSEL driver IC and the VCSEL IC having increased lengths, which can increase the inductance of the paths. This increase in inductance degrades signal integrity and can result in an increase in electromagnetic interference (EMI). In addition, in order to increase the distance between the VCSEL driver IC and the VCSEL IC, it may be necessary to increase the overall size of the transceiver module, which is generally undesirable for a variety of reasons.
The connector holds the optical fibers and mates with the transceiver module has one, but typically two or more, locking mechanisms that mate with locking mechanisms on the transceiver module to secure the connector to the transceiver module. The mating should be very precise so that the ends of the optical fibers held in the connector are aligned with the optics systems of the transceiver module when the connector is secured to the transceiver module. If the mating is not extremely precise, the optical alignment also will not be extremely precise, and performance will suffer. A variety of transceiver modules and connectors exist that are configured to mate very precisely and provide very precise optical alignment between the laser diodes, the optics system and the transmit fiber ends on the transmit side and between the receive fiber ends, the optics system and the receive photodiodes on the receive side. One problem associated with many existing designs is that heat generated by the ICs of the transceiver module causes the components of the optics systems and other components of the transceiver module and/or of the connector to expand. This expansion can result in problems with the optical alignment, which can degrade performance.
It would be desirable to provide a transceiver module having a design that thermally isolates the laser diode driver IC from the laser diode IC without increasing the lengths of the electrical paths between the ICs. It would also be desirable to provide a transceiver module having a design in which the lengths of the electrical paths between the laser diode driver IC and the laser diode IC are reduced in order to improve signal integrity and reduce EMI. It would also be desirable to provide a transceiver module having a design that ensures that precise optical alignment on the transmit side and receive side of the transceiver module is maintained despite any heat generated by one or more of the ICs of the transceiver module.